[client] refactor lazy detection

[pappz]

Describe your changes

This PR introduces a new inactivity package responsible for monitoring peer activity and notifying when peers become inactive.
Introduces a new Signal message type to close the peer connection after the idle timeout is reached.

• Periodically checks the last activity of registered peers via a Bind interface.
• Notifies via a channel when peers exceed a configurable inactivity threshold.

Default settings

DefaultInactivityThreshold is set to 15 minutes, with a minimum allowed threshold of 1 minute.

Limitations

This inactivity check does not support kernel WireGuard integration. In kernel–user space communication, the user space side will always be responsible for closing the connection.

Issue ticket number and link

Stack

Checklist

• [ ] Is it a bug fix
• [ ] Is a typo/documentation fix
• [x] Is a feature enhancement
• [x] It is a refactor
• [ ] Created tests that fail without the change (if possible)
• [ ] Extended the README / documentation, if necessary

By submitting this pull request, you confirm that you have read and agree to the terms of the Contributor License Agreement.